Fiber optic system for in vivo real-time determination of tissue optical properties from steady-state diffuse reflectance measurements

We present a versatile and compact fiber optic probe for real-time determination of the absorption and the reduced scattering coefficients from spatially resolved continuous wave diffuse reflectance measurements. The probe collects the diffuse reflectance at six distances in the range 0.6-7.8 mm at four arbitrary wavelengths, which were 660, 785, 805, and 974 nm in these experiments. The maximum sampling rate for one cycle of measurements including all four wavelengths is about 100 Hz. The absorption and the reduced scattering coefficients are extracted real-time from the probe measurements using multivariate calibration methods based on multiple polynomial regression and Newton-Raphson algorithms. The system was calibrated on a 6×7 matrix of Intralipid/ink phantoms with optical properties within typical biological ranges, e.g. at 785 nm, the ranges of the absorption and the reduced scattering coefficients, were 0-0.3/cm and 6-16/cm, respectively. Cross-validation tests shoved that the mean prediction error, relative to the ranges of absorption and the reduced scattering coefficients were 2.8% and 1.3%, respectively.